1. Field of Invention
The present invention generally relates to medical robotic systems and in particular, to a medical robotic system providing coupled control modes.
2. Background Art
Minimally invasive surgery is known under various names (e.g., endoscopy, laparoscopy, arthroscopy, endovascular, keyhole, etc.), often specific to the anatomical area in which work is done. Such surgery includes the use of both hand-held and teleoperated/telemanipulated/telepresence (robot assisted/telerobotics) equipment, such as the da Vinci® Surgical System made by Intuitive Surgical, Inc. of Sunnyvale, Calif. Both diagnostic (e.g., biopsy) and therapeutic procedures (“medical procedures”) are done. Instruments may be inserted into a patient percutaneously via surgical incision or via natural orifice. A new, experimental minimally invasive surgery variation is Natural Orifice Transluminal Endoscopic Surgery (NOTES), in which instruments enter via a natural orifice (e.g., mouth, nostril, ear canal, anus, vagina, urethra) and continue to a surgical site via a transluminal incision (e.g., in a gastric or colonic wall) within the body. Although teleoperative surgery using the da Vinci® Surgical System provides great benefits over, for instance, many hand-held procedures, for some patients and for some anatomical areas the da Vinci® Surgical System may be unable to effectively access a surgical site. In addition, further reducing the size and number of incisions generally aids patient recovery and helps reduce patient trauma and discomfort.
Various slave manipulators are provided in such medical robotic systems to perform useful functions, such as manipulating instruments to perform medical procedures on a patient, positioning and orienting imaging systems such as endoscopic imaging devices to capture images of the instruments' working ends, and delivering the working ends of the instruments and an image capturing end of the imaging system to a work site in the patient. The delivery of the working and image capturing ends of the instruments and imaging system (“medical devices”) uses one or more guide tubes and structures that hold and manipulate the guide tube(s). In addition, master manipulators are used as input devices to track the motion of their operator's hands and to provide appropriate haptic feedback to the operator indicative of the state of their associated slave manipulators. Depending on their respective function, the slave and master manipulators (“robotic manipulators”) may be designed with different workspaces and dexterities.
In general, the reachable workspace of a medical device that is being manipulated by a slave manipulator is the set of points and orientations in space that its distal tip (e.g., working or image capturing end) can reach. On the other hand, the dexterous workspace of the medical device's distal tip generally identifies the set of points in space that can be reached by primarily changing its orientation (e.g., changing the position of a wrist joint that orients the distal tip). As explanation, dexterity is a measure of the capability of a robotic manipulator to control the position (in a limited manner) and orientation of the working end of its associated medical device. Further, it relates the joint degrees of freedom (i.e. the number of independently actuated joints in a kinematic chain of the robotic manipulator/medical device) and the Cartesian/output degrees of freedom that describe the independent rigid body positions and orientations of the distal tip. While the number of output (slave manipulator) degrees of freedom (DOF) is often at most six, the number of input (master manipulator) joint DOFs varies greatly depending on the master manipulator design
As may be readily appreciated, the dexterous workspace is generally a subset of the reachable workspace. To enable the surgeon to finely control working ends of the instruments, instrument slave manipulators are generally designed to optimize their dexterity, even at the expense of sacrificing their overall reachable workspace. To compensate for such limitation, a base manipulator (such as a patient side cart) with a large reachable workspace may be used to deliver the instrument and imaging system slave manipulators near the entry apertures (e.g., minimally invasive incisions or natural orifices) in the patient body. Further, when the instruments and imaging system are disposed within a common guide tube, the guide tube serves as a secondary base since movement of the guide tube in this case effectively moves all of the instruments and the imaging system disposed therein. The instrument and imaging system slave manipulators may then finally deliver the working and image capturing ends of their respective medical devices to the work site (e.g., target anatomy) in the patient.
The overall capability of a medical robotic system is achieved by a balance between the workspace and dexterity of all the robotic manipulators that constitute it. However, the differences in the individual capabilities of each manipulator have to be clear and well understood by the user in order to effectively utilize the system. It is in general difficult for the user to select which manipulator to control from the console and how to move it in order to achieve a desired “working configuration” of their respective medical devices inside the patient, with the instruments' working ends having the best possible dexterity and reach, while the capturing end of the imaging system is positioned in such a way to provide good visualization of the medical procedure being performed at the work site without interfering with the instruments' movements. Hence, it is desirable to provide the system with the capability of performing secondary or coupled control movements, e.g., for the camera manipulator and the base manipulator (guide tube manipulator and/or manipulator for moving the setup arms and or support for the patient side support system), so as not to distract the user from performing the medical procedure at the time using the surgical instruments.
The number of degrees of freedom (DOFs) is the number of independent variables that uniquely identify the pose/configuration of a system. Since robotic manipulators are kinematic chains that map the (input) joint space into the (output) Cartesian space, the notion of DOF can be expressed in any of these two spaces. In particular, the set of joint DOFs is the set of joint variables for all the independently controlled joints. Without loss of generality, joints are mechanisms that provide a single translational (prismatic joints) or rotational (revolute joints) DOF. Any mechanism that provides more than one DOF motion is considered, from a kinematic modeling perspective, as two or more separate joints. The set of Cartesian DOFs is usually represented by the three translational (position) variables (e.g., surge, heave, sway) and by the three rotational (orientation) variables (e.g. Euler angles or roll/pitch/yaw angles) that describe the position and orientation of an end effector (or tip) frame with respect to a given reference Cartesian frame.
For example, a planar mechanism with an end effector mounted on two independent and perpendicular rails has the capability of controlling the x/y position within the area spanned by the two rails (prismatic DOFs). If the end effector can be rotated around an axis perpendicular to the plane of the rails, then there are then three input DOFs (the two rail positions and the yaw angle) that correspond to three output DOFs (the x/y position and the orientation angle of the end effector).
Although the number of Cartesian DOFs is at most six, a condition in which all the translational and orientational variables are independently controlled, the number of joint DOFs is generally the result of design choices that involve considerations of the complexity of the mechanism and the task specifications. Accordingly, the number of joint DOFs can be more than, equal to, or less than six. For non-redundant kinematic chains, the number of independently controlled joints is equal to the degree of mobility for the end effector frame. For a certain number of prismatic and revolute joint DOFs, the end effector frame will have an equal number of DOFs (except when in singular configurations) in Cartesian space that will correspond to a combination of translational (x/y/z position) and rotational (roll/pitch/yaw orientation angle) motions.
The distinction between the input and the output DOFs is extremely important in situations with redundant or “defective” kinematic chains (e.g., mechanical manipulators). In particular, “defective” manipulators have fewer than six independently controlled joints and therefore do not have the capability of fully controlling end effector position and orientation. Instead, defective manipulators are limited to controlling only a subset of the position and orientation variables. On the other hand, redundant manipulators have more than six joint DOFs. Thus, a redundant manipulator can use more than one joint configuration to establish a desired 6-DOF end effector pose. In other words, additional degrees of freedom can be used to control not just the end effector position and orientation but also the “shape” of the manipulator itself. In addition to the kinematic degrees of freedom, mechanisms may have other DOFs, such as the pivoting lever movement of gripping jaws or scissors blades.
It is also important to consider reference frames for the space in which DOFs are specified. For example, a single DOF change in joint space (e.g., the joint between two links rotates) may result in a motion that combines changes in the Cartesian translational and orientational variables of the frame attached to the distal tip of one of the links (the frame at the distal tip both rotates and translates through space). Kinematics describes the process of converting from one measurement space to another. For example, using joint space measurements to determine the Cartesian space position and orientation of a reference frame at the tip of a kinematic chain is “forward” kinematics. Using Cartesian space position and orientation for the reference frame at the tip of a kinematic chain to determine the required joint positions is “inverse” kinematics. If there are any revolute joints, kinematics involves non-linear (trigonometric) functions.